Machine tools are compact and inexpensive, and can be coupled with various application tools, such as grinding discs, emery wheel machines, drilling machines, electric wrenches and the like, to form diversified types to assist operators in performing varying tasks. Therefore, machine tools are very popular.
The conventional machine tool comprises a body, a circuit board arranged inside the body, a motor driven by the circuit board, and a tool shaft rotated by the motor. When the circuit board drives the motor and the tool shaft to rotate, an action element installed on the tool shaft is also driven to operate and machine a workpiece. As the motor of the machine tool is encased in a relatively closed casing, heat generated by the motor is hard to be dissipated. The accumulated heat is likely to overheat the motor and impact the operation of the machine tool. Thus, many heat dissipation structures had been developed to dissipate heat generated by the motor of the machine tool. U.S. Pat. No. 6,789,630 and No. 7,166,939 disclose heat dissipation structures, wherein fan blades or radiation fins are installed on the axis and rotated by the motor to generate airflow to cool the motor. A China patent No. CN201478938 discloses a heat dissipation structure, wherein heat dissipation openings are arranged at a position corresponding to the motor to dissipate heat generated by the motor.
In addition to the motor, control chips and other ICs on the circuit board also generate heat. Thus, the circuit board also needs a heat dissipation mechanism to dissipate heat. A U.S. Pat. No. 7,699,687 discloses a hand-held grinding machine including a housing, a tool shaft arranged inside the housing, a motor installed on the tool shaft, a handle installed on the housing, and a circuit board arranged inside the handle. The handle has a plurality of heat-dissipation holes formed at a position corresponding to the circuit board to dissipate heat generated by the circuit board.
When machining a workpiece, the machine tool usually generates much dust, and the dust is likely to enter the machine tool via the heat dissipation holes and adhere to the circuit board, which may damage the electronic elements on the circuit board and disable the machine tool from operating.